Presently, vehicles are spread that incorporate a storage battery in addition to a battery. Such a vehicle incorporates a converter stepping up and down the output voltage of the battery so as to convert the output voltage and then applying the converted voltage on the storage battery.
A converter known in conventional art is a converter comprising: an inductor; a first switch and a second switch, one end of each of which is connected to one end of the inductor; a third switch, one end of which is connected to the other end of the inductor; and a fourth switch, one end and the other end of which are connected respectively to the other ends of the inductor and the second switch, and turning ON/OFF individually the first switch, the second switch, the third switch and the fourth switch so as to convert a voltage between the other ends of the first switch and the second switch.
In this converter of conventional art, a battery is connected between the other ends of the first switch and the second switch and a storage battery is connected between the other ends of the third switch and the fourth switch. Then, the first switch, the second switch, the third switch, and the fourth switch are turned ON/OFF individually so that the output voltage of the battery is converted. Then, the converted voltage is outputted to the storage battery.
When the output voltage of the battery is to be stepped down, in a state that the third switch and the fourth switch are maintained at ON and OFF respectively, transition is made alternately between a state that the first switch and the second switch are ON and OFF and a state that the first switch and the second switch are OFF and ON.
Here, when the second switch is turned ON for the purpose of stepping down the output voltage of the battery, a possibility arises that an electric current flows from the storage battery, that is, from the output side of the voltage, to the inductor so that the output voltage of the battery is not appropriately converted.
As such, a converter capable of avoiding adverse flow of an electric current from the output side of the voltage to the inductor is disclosed in Japanese Patent Application Laid-Open No. 2012-205427.
In the converter described in Japanese Patent Application Laid-Open No. 2012-205427, semiconductor switches are employed for the first switch, the second switch, the third switch, and the fourth switch. Then, a parasitic diode is connected between both ends of each of the first switch, the second switch, the third switch, and the fourth switch. In one parasitic diode, the anode is connected to one end of the third switch and the cathode is connected to the other end of the third switch.
In the converter described in Japanese Patent Application Laid-Open No. 2012-205427, when the output voltage of the battery is to be stepped down, in a state that the third switch is maintained at OFF, the first switch, the second switch, and the fourth switch are turned ON/OFF individually so that the output voltage is converted. Thus, the parasitic diode prevents adverse flow of an electric current from the storage battery to the battery.